Abstract
Aimed at the molding of polymer nanostructure parts, the interface model between long- and short-chain polycarbonates (PC) and nickel mold inserts was established by the molecular dynamics method. The molecular mechanism of the replication capability of polymer nanostructure part molding was discussed by analyzing the migration and diffusion of the molecular chain, concentration profile, filling morphology evolution, interface binding energy, and filling rate of conventional injection molding (CIM) and rapid heat cycle molding (RHCM). The results show that nanostructures are filled mainly during the packing stage. A short-chain PC system has a low glass transition temperature (Tg) and viscosity, good fluidity, and a high filling rate, so the replication capability of its nanostructures is good. A long-chain PC system has a fast cooling rate in CIM, its molecular chain motion is blocked, the filling rate is low, and the interface binding energy is small, and so its nanostructures have poor replication capability. However, the high temperature at the nanostructures can be maintained for a long time in RHCM, which promotes Brownian motion in the molecular chains. Under the action of packing pressure, molecular chains can overcome entanglement barriers and viscous resistance. Thus, the polymer concentration profile and filling rate increase with increasing packing pressure, which can produce more van der Waals energy. Furthermore, the evolution process of polymer filling morphology is realized by the Brownian motion of chain segments under packing pressure; that is, the diffusion motion of the molecular chain along the direction of a tube composed of other chains around it. With the increase of temperature or pressure, the migration and diffusion of the molecular chain can be promoted; thus, the replication capability of nanostructure parts for mold cavities can be enhanced.
Highlights
Injection molding technology has become one of the main methods of mass polymer material molding due to the advantages of its short molding cycle, low-cost, and high precision [1,2,3]
Zhou et al used PMMA as research materials, applied molecular dynamics method to study the polymer filling into nanocavity by injection molding, and elucidated the effects of molecular weight and cavity size on the filling behavior and final replication quality of nanostructures [19]
The nanostructure molding mechanism of long and short-chain polymer systems in conventional injection molding (CIM) and rapid heat cycle molding (RHCM) was discussed, and the filling morphology evolution in nanostructures and the reason for the high–low filling rate were analyzed to provide a theoretical basis for further improving the replication capability of nanostructures and improving the quality of nanostructure parts
Summary
Injection molding technology has become one of the main methods of mass polymer material molding due to the advantages of its short molding cycle, low-cost, and high precision [1,2,3]. Zhou et al used PMMA as research materials, applied molecular dynamics method to study the polymer filling into nanocavity by injection molding, and elucidated the effects of molecular weight and cavity size on the filling behavior and final replication quality of nanostructures [19]. The nanostructure molding mechanism of long and short-chain polymer systems in CIM and RHCM was discussed, and the filling morphology evolution in nanostructures and the reason for the high–low filling rate were analyzed to provide a theoretical basis for further improving the replication capability of nanostructures and improving the quality of nanostructure parts
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